I took a metal sheet(aluminium), placed the MCU over it so that all the pins gets shorted in the metal sheet. I also connected the metal sheet to electrical ground of my home. Is it sufficient or something else is needed? ).
If you "charge" a chip in free air and then "discharge" it to ground, the chip will not be harmed by the charge, but blow on the discharge. You can NOT avoid anything by "discharging" chips ONLY by not charging them.

Also, I throughly avoid styrofoam case for storing any IC
That is good, but what is wrong with the antistatic tubes/trays the chips come in? There are other materials than styrofoam that can generate static. The suppliers know what to ship in, why not use that. If you receive any chips in anything but antistatic tubes/antistatic trays/antistatic foam/anstistatic bag, return them. For antistatic foam, unless it is in a small plastic box with a manufacturers name on it do not believe.

Erik